Properly memoize ChangeAccess#validate_path_locks? to avoid excessive queries

Closes #4488

changelogs/unreleased-ee/sh-strong-memoize-validate-path-locks.yml

+---
+title: Properly memoize ChangeAccess#validate_path_locks? to avoid excessive queries
+merge_request:
+author:
+type: performance

lib/gitlab/checks/change_access.rb

@@ -2,6 +2,7 @@ module Gitlab
   module Checks
     class ChangeAccess
       include PathLocksHelper
+      include Gitlab::Utils::StrongMemoize
 
       ERROR_MESSAGES = {
         push_code: 'You are not allowed to push code to this project.',
@@ -300,9 +301,11 @@ module Gitlab
       end
 
       def validate_path_locks?
-        @validate_path_locks ||= @project.feature_available?(:file_locks) &&
-          project.path_locks.any? && @newrev && @oldrev &&
-          project.default_branch == @branch_name # locks protect default branch only
+        strong_memoize(:validate_path_locks) do
+          @project.feature_available?(:file_locks) &&
+            project.path_locks.any? && @newrev && @oldrev &&
+            project.default_branch == @branch_name # locks protect default branch only
+        end
       end
 
       def path_locks_validation

spec/lib/gitlab/checks/change_access_spec.rb

@@ -319,6 +319,12 @@ describe Gitlab::Checks::ChangeAccess do
           it 'allows the default branch even if it does not match push rule' do
             expect { subject.exec }.not_to raise_error
           end
+
+          it 'memoizes the validate_path_locks? call' do
+            expect(project.path_locks).to receive(:any?).once.and_call_original
+
+            2.times { subject.exec }
+          end
         end
       end